The phenotypic plasticity of vascular smooth muscle cells (SMCs) permits this muscle cell lineage to subserve diverse functions including the maintenance of arterial tone via contraction- relaxation and vessel wall integrity by proliferation and synthesis of extracellular matrix. By differentially regulating the expression of distinct sets of SMC lineage-specific genes, SMCs can modulate their phenotype from primarily contractile to primarily synthetic. However, relatively little is currently understood about the molecular mechanisms that control SMC-specific gene expression. One approach to understanding the molecular mechanisms that regulate SMC differentiation is to identify and characterize the cis-acting sequences and trans-acting factors that control SMC-specific transcription. Because of its SMC lineage-restricted pattern of expression, we have used the murine SM22alpha gene as a model system to examine the mechanisms that control SMC-specific gene expression. Preliminary studies demonstrated that SM22alpha is one of the earliest developmental markers of the SMC lineage. Moreover, the 280-bp SM22alpha promoter directs arterial SMC lineage-restricted gene expression in transgenic mice. This transcriptional regulatory element contains previously undescribed nuclear protein binding sites that bind lineage-restricted trans-acting factors. These data support the hypothesis that novel SMC lineage- restricted transcription factors control the expression of the SM22alpha gene in SMCs. The proposed studies are designed to elucidate the molecular mechanisms that control the SMC-specific pattern of SM22alpha gene. The specific aims of these studies are to: (i) identify the cis-acting elements that control activity for the arterial SMC-specific SM22alpha promoter during embryonic and postnatal development, (ii) characterize the trans-acting factors that regulate expression of the SM22alpha gene, (iii) examine the molecular mechanisms underlying activity of positive and negative regulatory factors on SM22alpha promoter activity, and (iv) clone and characterize SMC-specific transcription factors that regulate activity of the SM22alpha gene in SMCs should fundamentally increase understanding of SMC development and differentiation. As such, the proposed studies are relevant to understanding the pathogenesis of atherosclerosis and restenosis following balloon angioplasty.